1. Field of the Invention
This invention relates to igniters suited for use in air bag applications, and to air bag assemblies equipped with the igniters. More particularly, this invention relates to air bag igniters comprising a foamed igniter material.
2. Description of the Related Art
One important use for specifically formulated gas generating chemical compositions is in the operation of inflatable safety restraint systems, commonly referred to as air bag assemblies. Air bag assemblies are gaining in industrial and commercial acceptance to the point that many, if not most, new automobiles are equipped with such devices. Indeed, many new vehicles are equipped with multiple air bags to protect the driver and passengers, and contain multiple air bags for protection of each occupant.
Upon actuation of a vehicle""s supplemental (or secondary) restraint system upon impact of the vehicle in an accident or the like, sufficient gas must be generated to fully inflate the air bag of the supplemental restraint system before the driver would otherwise be thrust against the steering wheel or dashboard. Generally, the air bag must be inflated within a fraction of a second. As a consequence, nearly instantaneous gas generation is required.
Typically, generation of the amount of gas necessary for inflating an air bag is achieved through a sequential ignition of specifically formulated compositions. This chain commonly begins with a squib comprising two spaced-apart electrical terminals and a high-resistance yet conductive material connecting the terminals. Upon application of a predetermined amount of electrical energy to the electrical terminals, the squib generates heat sufficient to fire an igniter material positioned in operative relation with the squib. The ignited igniter material in turn ignites a gas generating material, often in the form of pellets, present in sufficient amounts to generate the gas to fully inflate the air bag, or deploy the inflating gas as in a so-called hybrid system. Suitable gas generating materials and air bag constructions are well known to those skilled in the art. For example, it has been known to use sodium azide gas generants, although others are known and contemplated within the scope of this invention.
Boron potassium nitrate (BKNO3) granules have conventionally been used as the igniter material. However, a drawback of the BKNO3 granules is that they tend to become friable or brittle when subjected to continued application of loads or pressures over extended periods of time. The deterioration of the granules increases the burn rate of the BKNO3, and may lead to over-pressurization during ignition, which can adversely affect performance.
It would therefore be a significant advancement in the art to provide an igniter material that is relatively insensitive to high impact loads.
It is, therefore, an object of this invention to provide an igniter composition that addresses a long-felt need in the art by addressing the aforementioned drawbacks associated with conventional igniter materials.
In accordance with the principles of this invention, these and other objects are attained with the inventive air bag igniter, which comprises a foamed material.
In accordance with a first embodiment of this invention, the foamed material is formulated from a composition comprising, as ingredients, at least one polyfunctional isocyanate, at least one non-energetic curable binder having a plurality of functional groups which are reactive with the polyfunctional isocyanate, at least one fuel source, at least one oxidizer, and at least one foaming agent which imparts porosity to the foamed material and may or may not be retained in the foamed material.
In accordance with a second embodiment of this invention, the foamed material is formulated from a composition comprising, as ingredients, at least one polyfunctional isocyanate, one or more energetic curable binders having a plurality of functional groups which are reactive with the polyfunctional isocyanate, one or more fuel sources other than the energetic curable binder(s), at least one oxidizer, and at least one foaming agent which imparts porosity to the foamed material and may or may not be retained in the foamed material.
In accordance with a third embodiment of this invention, the foamed material is formulated from a composition like that of the second embodiment, with the exception of being free of any fuels other than the energetic polymeric binder.
It is also an object of this invention to provide an air bag assembly that can be fired with a high confidence and consistent predictability. In accordance with the principles of this invention, this and other objects of the invention are attained by the provision of an air bag assembly comprising a gas generant (e.g., gas generating pellets) and at least one of the above-described air bag igniters in cooperative association with the gas generant so as to allow for ignition of the gas generant with high reliability. This invention also relates to vehicles, such as cars, sports utility vehicles, and trucks, comprising the air bag assembly positioned either (a) in a front position to protect the vehicle occupants from collision against the instrument panel or (b) in a side position to protect the vehicle occupants from impact against the door panel and/or compartment ceiling.
These and other objects, features, and advantages of the present invention will become apparent from the accompanying drawings and following detailed description which illustrate and explain, by way of example, the principles of the present invention.